A well-preserved Tyrannosaurus rex
femur turned up seven fragments of protein. Three of those fragments matched
fragments found in modern chickens, supporting an evolutionary link between
dinosaurs and birds. Image is copyright of Science.

The family tree of an infamous dinosaur
is coming to life before researchers' eyes. Scientists say they extracted protein
from a 68-million-year-old Tyrannosaurus rex leg bone that supports a
genetic link between dinosaurs and birds.

Organic material degrades over time. For example, protein
collagen breaks down in skin, leaving human faces with age-revealing smile lines
and crow's feet. But exactly how long cells and molecules take to degrade, particularly
in fossils, has been debated. Lab and theoretical experiments have suggested
that some proteins could last up to 1 million years, "but probably not
to the age of dinosaurs," said Mary Schweitzer, a paleobiologist at North
Carolina State University at an April 12 press conference. Schweitzer and colleagues'
discovery of collagen in a 68-million-year-old dinosaur, described Friday in
two papers in Science, confirms that small amounts of such material can
survive and perhaps are only now being detected because of increasingly precise
molecular analysis technologies.

Friday's description of T. rex protein follows Schweitzer
and colleagues' discovery two years ago of the only known well-preserved T.
rex soft tissue. The tissue was taken from the same dinosaur, which was
excavated in eastern Montana (see Geotimes online, Web
Extra, March 25, 2005). Although the team could describe the morphology
of the tissue's microstructures, including blood vessels that looked strikingly
similar to those of an ostrich, "we could not directly address what the
material was made of," Schweitzer said.

To determine how well the tissue was preserved, Schweitzer
and colleagues subjected the tissue to a slew of mineral, molecular and chemical
analyses, which turned up small, almost undetectable amounts of material that
had all the characteristics of collagen  an identifiable and relatively
hardy protein. Next, the team turned extracts of the sample over to John Asara,
director of the mass spectrometry facility at Beth Israel Deaconess Medical
School in Boston. Asara had developed a highly sensitive method using mass spectrometry
to sequence protein from various cancer patients to try to identify how the
disease spreads to other tissues. The device's sensitivity should be able to
determine the sequence of amino acids within the T. rex collagen, the
team suggested. If successful, the sequence could then be compared to sequences
of modern animals.

The tests worked. Asara found the amino acid sequences for
seven fragments of the collagen protein, three of which most closely matched
those of modern chickens. The remaining sequences matched a mix of other animals,
including a frog and a newt. The finding supports previous evidence that birds
evolved from dinosaurs or that they are closely related, Asara said.

No sequence was unique to T. rex, however, which would have "verified
completely" that the sequence was not modern and thus not the result of
contamination, Schweitzer said. Unique sequences are "like a fingerprint,"
Schweitzer told Geotimes, and also provide more information about an
animal's evolutionary history. The researchers were sucessful, however, in finding
unique sequences from samples from a younger fossil from a mastodon. This fossil
leg bone, which could be as much as 600,000 years old, turned up more than 70
sequences, four of which were unique to the mastodon. Identifying a specific
amino acid at a particular location in the collagen can identify it as belonging
to mastodon.

Derek Briggs, a paleobiologist at Yale University says he
is not surprised that the mastodon leg bone had preserved protein sequences,
as previous research has already found intact mastodon DNA gene sequences, which
are even more delicate. But protein that has survived 68 million years in T.
rex is "extraordinary," he says.

Still, Briggs says that the discovery would be more useful
if it were known what happens to proteins in other animals in the millions of
years between the time of T. rex and the mastodon. "That would demonstrate
how potentially powerful [the finding] is, and if it's more widespread than
we imagined."

The key lies in getting specimens that are "genuinely
well-preserved," said Jack Horner of Montana State University, speaking
at the press conference. Horner co-authored one of last week's papers on the
tissue and led the team that excavated the T. rex fossils in 2003 from
beneath 1,000 cubic meters of sandstone. "I think we are going to find
that many specimens are like this," he says. "I don't think that this
is unique in any way. I think it's just going to be a matter of paleontologists
taking a little extra time and getting into sites that are not necessarily easy
to excavate."